Monday, April 22, 2013

Push-Dose Phenylephrine: Experience and Important Points

Originating in anesthesia, promoted in emergency medicine by and EMRAP, the utilization of push dose pressors has been growing. While there doesn’t exist much data to back up its use, I think the clinical experience speaks for itself.  In my experience has been generally good with recommending push dose phenylephrine aka. “Neostick,” if the dose is appropriate (80-100 mcg, not 20mcg) and the timing is appropriate (not after hours of hypotension).  Likewise, expectations of response differ depending on the clinical scenario; from buying a few minutes to allow for central line placement, or increasing SBP by about 5-10 mmHg.

The actual compounding of the Neostick is important to discuss both with everyone in the ED on your team.  I’ve had to review cases where the intent was to use push dose epinephrine, but due to poor (or lack of) communication, the entire syringe was pushed instead of 1 mL.  If you have pharmacists in your ED, get them involved early, or better yet, before considering push dose pressors.  They can inform you regarding hospital policy for IV mixing outside of the pharmacy, how they would recommend mixing the pressor syringe, or the availability of commercially premade syringes.

While compounding instructions exist on other sites, I have my own method. I’ve adapted to the method describe below as a result of poor response during my initial experience with push dose pressors, even at relatively high doses of phenylephrine.  I started to become concerned that the final concentration of phenylephrine in the syringe was not what was desired since I was mixing 1mL into a 100mL bag of NS.  Additionally, it is not widely known outside the walls of the pharmacy that commercially available IV piggyback bags contain various amounts of overfill. For example, in a 100mL NS contains approx. 109mL. So adding 1mL will make the total volume 110mL and therefore, a more dilute final concentration. In pharmacy there is a general rule that unless you are adding > 10% of the volume of the bag, you do not need to account for over fill. In this instance, however, since you’re withdrawing a small amount from the bag, which is highly dependent on the final concentration, the overfill must be taken into consideration.

The adapted method can be done in one of two ways. Again, discuss this within your own practice site to see which one others (and yourself) are comfortable with BEFORE being in a situation where a Neostick is needed STAT.

My method:
Step 1: To account for overfill and the volume to be administered, take a 100mL IVPB bag of NS, withdraw and waste 10mL.
Step 2: Add 1mL of phenylephrine 10mg/mL (from a vial). The concentration in the bag is now truly 10,000 mcg / 100mL (100 mcg/mL)

A more confusing method that I wouldn’t recommend doing if you aren’t an experienced pharmacist,

Method 2:
Step 1: Withdraw 1mL of phenylephrine (10mg/mL) in a 10 mL syringe.
Step 2: With the same syringe, draw up an additional 9mL of NS to a total volume of 10mL. Now you have a 10mg/10mL syringe.
Step 3: Next, waste 9mL from that syringe, leaving 1mL, or 1mg.
Step 4: Repeat the dilution in step 2, yielding a final concentration of 100mcg/mL. (1mg in 10mL syringe or 1000 mcg/10mL)

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